"We will take action against any crime that's committed," said Capt. Chris Fowler. "And, specifically, with respect to May Day, crimes against property and, more importantly, crimes against persons."

There's reason to brace for trouble. Anarchist websites are urging protestors to shut down banks and other corporate businesses.

One call to action says, "Let's attack with all of the anger and strength amassed over the past year."

Organizers say the original meaning of May Day sometimes gets lost in these messages.

"This is the only opportunity that poor people, that working people have to voice their opinion," said Juan Bocanegra.

Bocanegra is organizing the Workers' Rights March, which has been disrupted in the past.

"And if there's people that want to disrupt that opportunity from poor and working people, then their goals and their objectives are totally misplaced," he said.

Bocanegra isn't planning any security changes, but downtown businesses are. Some have hired private security to protect store interiors, while a large police presence will offer a show-of-force on surrounding streets.

"I think we're ready," Fowler said.

Police say they plan to strike a balance between letting people exercise their free speech rights, while also preventing any criminal acts.

They plan to let people march -- and likely even be disruptive -- but the first sign of damage will cross the line.